CVE-2021-33056: Belledonne Belle-sip before 4.5.20, as used in Linphone and other products, can crash via an invalid From head

Q: How do I fix CVE-2021-33056?

belle-sip: upgrade to 4.5.20. Exact commands for each OS are on this page.

Q: Is CVE-2021-33056 being exploited?

CVE-2021-33056 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-33056 affect?

CVE-2021-33056 affects belle-sip. Severity is high (CVSS 7.5). Belledonne Belle-sip before 4.5.20, as used in Linphone and other products, can crash via an invalid From header in a SIP message.

Q: How urgent is CVE-2021-33056?

Priority 49/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2021-33056 is a high-severity flaw (CVSS 7.5) affecting belle-sip. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Belledonne Belle-sip before 4.5.20, as used in Linphone and other products, can crash via an invalid From header in a SIP message.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.3% (top 30%)
CISA exploited list	No
Weakness	CWE-444
Published	2021-08-12
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: linphone

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-08-12 21:15 UTCPublished CVE record published
2026-06-17 03:54 UTCUpdated Record last modified

linphone belle-sip UPGRADE

Affected: < 4.5.20

Fixed in: 4.5.20

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy belle-sip || rpm -q belle-sip || belle-sip --version

2. UPGRADE to 4.5.20 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade belle-sip

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade belle-sip

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-33056?

belle-sip: upgrade to 4.5.20. Exact commands for each OS are on this page.

Is CVE-2021-33056 being exploited?

CVE-2021-33056 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-33056 affect?

CVE-2021-33056 affects belle-sip. Severity is high (CVSS 7.5). Belledonne Belle-sip before 4.5.20, as used in Linphone and other products, can crash via an invalid From header in a SIP message.

How urgent is CVE-2021-33056?

Priority 49/100. High severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2021-43611 HIGH 7.5 UPGRADE Belledonne Belle-sip before 5.0.20 can crash applications such as Linphone via " \ " in the display name of a
CVE-2021-43610 HIGH 7.5 UPGRADE Belledonne Belle-sip before 5.0.20 can crash applications such as Linphone via an invalid From header (request

References

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